STUDIES ON ETHYLENE ADSORPTION ON NI, PD AND PT FILMS AND THE REACTIVITY OF THE SELECTED FORMS OF THE ADSORBATE WITH HYDROGEN

A rapidly-recording, static-capacitor method was used to study surface potential changes that occur during ethylene adsorption on Ni, Pd, and Pt films at 298 K. A precise dosing system for the introduction of gases and a careful determination of the roughness factor allowed us to relate the surface potential to the concentration of the various adsorbed species. Using this information we propose a mechanism for ethylene selfhydrogenation. Ethylene admolecules adsorbed in the second layer react readily with hydrogen whereas those from the first layer do not. On platinum films, only the electropositively-polarised β+ hydrogen adatoms are reactive with ethylene, but with Ni and Pd films only the electronegatively-polarised β- hydrogen adatoms are reactive. © 1979.